Number to Words Convertor

numberToWords.js

import { toWords } from 'number-to-words';

export function numberToWords(number) {
  if (!number || number === true) {
    return number;
  }

  const numWithNoNonDigits = number.replace ? number.replace(/\D/g,'') : number;
  const numToArray = numWithNoNonDigits.toString().split('');

  if (Number.isNaN(parseInt(numWithNoNonDigits))) {
    return number;
  }

  let result = '';

  numToArray.forEach((item, index, array) => {
    if (index !== array.length - 1) {
      result += `${toWords(item)} `;
    }
    else {
      result += `${toWords(item)}`;
    }
  });

  return result;
}

numberToWords.spec.js

import { numberToWords } from './numberToWords';

describe('numberToWords', () => {
    it('should return words for an international number string', () => {
      const INPUT = '+44 000 123 456';
      const EXPECTED = 'four four zero zero zero one two three four five six';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should return words for a local number string', () => {
      const INPUT = '0800 000 1234';
      const EXPECTED = 'zero eight zero zero zero zero zero one two three four';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should return words for a number', () => {
      const INPUT = 123;
      const EXPECTED = 'one two three';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should return words for a mixture of letters and numbers', () => {
      const INPUT = 'nice123nice';
      const EXPECTED = 'one two three';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should fallback gracefully for no input', () => {
      const INPUT = '';
      const EXPECTED = '';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should fallback gracefully for just a plus symbol', () => {
      const INPUT = '+';
      const EXPECTED = '+';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should fallback gracefully for a non-number', () => {
      const INPUT = 'nice';
      const EXPECTED = 'nice';
      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should fallback gracefully for a boolean: false value', () => {
      const INPUT = false;
      const EXPECTED = false;

      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should fallback gracefully for a boolean: true value', () => {
      const INPUT = true;
      const EXPECTED = true;

      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });

    it('should fallback gracefully for a NaN', () => {
      const INPUT = NaN;
      const EXPECTED = NaN;

      expect(numberToWords(INPUT)).toEqual(EXPECTED);
    });
  });